External compression of spinal cord through variety of sources including retrograde movement of a vertebral body or disc, a tumor, or a vascular malformation remains major causes of myelopathy. The external compression of the spinal cord leads to paraparesis, segmental sensory loss, and sometimes urinary and fecal incontinence.
In humans, the vertebral column is a column usually consisting of 33 vertebrae, the sacrum, intervertebral discs, and the coccyx situated in the dorsal aspect of the torso. The vertebral canal follows the different curves of the spinal column. It is large and triangular in those parts of the column which enjoy the greatest freedom of movement, such as the cervical and lumbar regions and is small and rounded in the thoracic region, where motion is more limited. The spinal cord is located inside the vertebral canal and extends from the foramen magnum down to the level of the first and second lumbar vertebrae (at birth, down to second and third lumbar vertebrae). The spinal cord is composed of 31 segments: 8 cervical (C), 12 thoracic (T), 5 lumbar (L), 5 sacral (S), and 1 coccygeal (Co), mainly vestigial. The spinal nerves comprise the sensory nerve roots, which enter the spinal cord at each level, and the motor roots, which emerge from the cord at each level, which is formed by the foramina of 7 cervical, 12 thoracic, 5 lumbar, and 5 sacral vertebrae, which together form the spine. The conus medullaris is the cone-shaped termination of the caudal cord. The pia mater continues caudally as the filum terminale through the dural sac and attaches to the coccyx. The coccyx has only one spinal segment. Several macroscopic grooves are discernible on the surface of the spinal cord. Most prominent is the anterior median fissure, which is occupied by the anterior spinal artery. The posterior median sulcus is less prominent. The anterior and posterior nerve rootlets emerge at the anterolateral and posterolateral sulci.
Within the vertebral canal, both spinal cord (CNS) and spinal roots (PNS) are enveloped by meninges. Spinal dura mater is separated from periosteum lining the vertebral canal by an epidural space that contains a variable amount of fat (in the cranial cavity, dura mater and periosteum merge so an epidural space does not exist). Three layers of meninges envelop the spinal cord and the roots of spinal nerves. The most superficial menix is dura mater. It is protective by virtue of its high collagen content. Arachnoid (arachnoid membrane) is thin and delicate, being composed of flattened fibrocytes and flimsy strands of collagen. In life, arachnoid contacts dura mater due to cerebrospinal fluid pressure within the subarachnoid space. Arachnoid trabeculae are delicate strands of arachnoid that traverse the subarachnoid space to join pia mater. The subarachnoid space filled with cerebrospinal fluid forms a space where devices can be advanced and deployed between the vertebral, disc, and external compression and spinal cord itself. Pia mater consists of flattened fibrocytes that line the subarachnoid space and collagen bundles in contact with glial cells at the surface of the spinal cord and spinal roots. Bilaterally, pia mater collagen is thickened to form denticulate ligaments. Processes of the ligaments periodically join dura mater and thus, within dura mater, the spinal cord is suspended by bilateral denticulate ligaments and thereby surrounded by protective cerebrospinal fluid within the subarachnoid space.
Spinal cord compression develops when the spinal cord is compressed by bone fragments from a vertebral fracture, a tumor, abscess, ruptured intervertebral disc or other lesion. It is regarded as a medical emergency independent of its cause, and requires swift diagnosis and treatment to prevent long-term disability due to irreversible spinal cord injury. Surgery is indicated in localized compression with or without postoperative radiation is delivered within 2-3 weeks of surgical decompression. Surgery usually comprises of a laminectomy to relieve pressure on the spinal cord or the nerve roots. The lamina is the bony roof of the spinal canal. Laminectomy is the term used to refer to the process of removing the lamina (usually both sides). Removing the lamina increases the size of the spinal canal, giving more room for the spinal cord or nerve roots. However, the process is extensive and is associated with complications such as bleeding within the operative sites, or worsening of neurological deficits.